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POSTSCRIPT, March 23: Comments on this review from 80 Plus / Ecos Consulting
RE: SilentPCReview's Testing of Enhance ENP-5136
March 23, 2006
Dear Silent PC Review readers,
After reading through Silent PC Review's recent review of the Enhance Electronics ENP-5136GH ATX12V power supply, the 80 PLUS® program thought it appropriate to comment on the test results presented on this 80 PLUS-certified product and provide some plausible reasons for the differences between SPCR's results and ours.
First, some background. Ecos Consulting (the firm that manages the 80 PLUS program) and EPRI Solutions, Inc. have been researching and measuring power supply efficiency for several years under funding from various non-profit and government sources. We have been developing a generalized test procedure to measure the efficiency of internal power supplies - such as computer power supplies - since February of 2004. The latest revision of this test procedure was recently presented at the Applied Power Electronics Convention (APEC) in Dallas, TX and can be found at www.EfficientPowerSupplies.org. We have used this method to test nearly 100 desktop computer and server power supplies, including those power supplies listed on www.80PLUS.org as certified under the 80 PLUS program. During this time we have also remained in touch with Mike Chin of SPCR for both his input on the test method and to share efficiency measurements.
Our data and SPCR's are usually in very close agreement, and for this reason we were rather surprised at SPCR's recent test results on the Enhance Electronics ENP-5136GH ATX12V model that passed 80 PLUS certification. The 80 PLUS program stands by its certification of this model, meaning that it is 80% efficient at 20%, 50%, and 100% load as measured using the test procedure described above. I would like to propose some of our latest thinking on why our data may not agree as a result of small but important deviations from the reference test procedure:
- Although SPCR has taken great care to reproduce the thermal environment of an actual PC through a thermal enclosure representative of a desktop tower case, this is technically not the same test setup that the 80 PLUS program would use to certify a power supply. As stipulated in our referenced test procedure, we test the power supplies on an open-air, thermally non-conductive test bench at an ambient temperature of 23 ºC and with an airflow no greater than 0.5 m/s near the bench (this is directly referenced from an international test standard, IEC 62301). A hotter thermal environment may cause certain power supply designs - potentially the ENP-5136GH as well - to exhibit different levels of efficiency when tested.
- We are well aware of the rigor with which SPCR tests and reviews products featured on its site and fully appreciate the lengths to which the reviewers have gone to obtain accurate power/efficiency measurements. However, when hundreds of watts are flowing through a power supply - up to 360 watts in the case of the Enhance Electronics product - small parasitic losses in test equipment that go unnoticed can result in very large changes in overall efficiency results. For example, at EPRI Solutions where all 80 PLUS power supplies are certified, test engineers have to account for the power dissipated through I2R losses in the power meter's test leads. At high levels of current, these leads taken together can dissipate several watts of power, severely impacting the accuracy of the overall measurement. If SPCR does not account for such losses, they might observe lower overall efficiency in some high-power, high-current tests.
Regardless of the small percent differences between our individual efficiency measurements, the 80 PLUS program would like to salute the efforts of SPCR, which has continued to provide its readers with thorough, in-depth, high-quality reviews of cool, quiet, and efficient computing products. As another recent SPCR article indicates, a small revolution is currently underway in the computer industry to provide computing services as efficiently as possible, all of which will help reduce thermals and keep machines running as quietly. Highly efficient computer power supplies will continue to be a part of the overall strategy, and we encourage silent PC enthusiasts to keep abreast of developments with the 80 PLUS program so that they are aware of the latest and most efficient computer power supply designs.
postendorp at ecosconsulting.com
80 PLUS Senior Program Manager
kdunn at ecosconsulting.com
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SPCR Forum discussion thread
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